Broadly speaking, aerosol spray devices comprise a container holding a liquid to be discharged together and an outlet nozzle associated with a valving arrangement which is selectively operable to allow discharge of the liquid as a spray from the nozzle by means of the propellant provided within the container.
Both “compressed gas propellant aerosols” and “liquefied gas propellant aerosols” are known. The former incorporate a propellant which is a gas at 25° C. and at a pressure of at least 50 bar (e.g. air, nitrogen or carbon dioxide). Such a gas does not liquefy in the aerosol spray device. On opening of the valving arrangement, the compressed gas “pushes” liquid in the spray device through the aforementioned nozzle that provides for atomisation. There are, in fact, two types of “compressed gas propellant aerosols”. In one type, only liquid from the container (“pushed-out” by the compressed gas) is supplied to the outlet nozzle. In the other principal type, a portion of the propellant gas from the container is bled into the liquid being supplied to the nozzle which atomises the resulting two-phase, bubble-laden (“bubbly”) flow to produce the spray. This latter format can produce finer sprays than the former.
In contrast, “liquefied gas propellant aerosols” use a propellant which is present (in the aerosol spray device) both in the gaseous and liquid phases and is miscible with the latter. The propellant may, for example, be butane, propane or a mixture thereof. On discharge, the gas phase propellant “propels” the liquid in container (including dissolved, liquid phase propellant through the nozzle).
It is well known that “liquefied gas propellant aerosols” are capable of producing finer sprays than “compressed gas propellant aerosols”. This is due to the fact that, in the former, a large proportion of the liquefied gas “flash vaporises” during discharge of liquid from the aerosol spray device and this rapid expansion gives rise to a fine spray. Such fine sprays cannot generally be achieved with “compressed gas propellant aerosols”, in either of the two principal formats described above.
Attempts have been made to improve the “fineness” of sprays generated by “compressed gas propellant aerosols”. Prior art proposals have included the possibility of “bleeding off” some of the compressed gas (e.g. nitrogen) that is present in the container and mixing this with the liquid product to achieve “two fluid atomisation” which is a technique known to provide fine sprays for other areas of spray technology, e.g. liquid fuel combustion. However it has been found extremely difficult to produce fine sprays using two fluid atomisation with aerosol spray devices, and the nearest approach has been to use the equivalent of a vapour phase tap (VPTs are used in “liquefied gas propellant aerosols”) to bleed some gas into the valve. However results for improving spray fineness have not been significantly beneficial.
PCT Patent Applications (Publication) Nos. WO 2011/061531 and WO 2011/128607, the contents of which are hereby incorporated by reference, each disclose aerosol spray devices for producing fine sprays in the case of “compressed gas propellant aerosols” (although there is some applicability also to “liquefied gas propellant aerosols”). Devices disclosed in WO 2011/061531 and WO 2011/128607 incorporate a spray discharge assembly incorporating a flow conduit for supplying fluid from a container to a spray outlet region of the device. The flow conduit has at least one first inlet for liquid from the container and at least one second inlet for propellant gas from a head space of the container. The spray discharge assembly further incorporates a valving arrangement such that movement of a valve stem from a first to second limit position opens the first and second inlets to cause a bubble laden flow to be generated in the flow conduit for supply to the spray outlet region. An aerosol device of this general type is illustrated in FIG. 1, which illustrates a known aerosol spray device 1 in the normal “rest” or “closed” position.
The device 1 comprises a pressurised container 2 on the top of which is mounted an spray discharge assembly 3 which, as schematically illustrated in the Figure, is crimped on to the top portion of container 2. Provided within container 2 is a liquid 5 to be dispensed from the device by a pressurised gas such as nitrogen, air or carbon dioxide, which has limited solubility in the liquid 5 and is in a head space 6 of the container 2. The gas in the head space 6 may, for example, be at an initial pressure of 9 to 20 bar depending upon the type of container in use. The initial pressure may, for example, be 9 or 12 bar. There are however higher pressure “standard” cans now available (but as yet little used), for which the initial pressure is for example 18 bar or higher. Such cans can also be used in the present invention. Higher initial can pressure is good because there is more mass of gas available to help atomisation and higher nozzle velocities which also helps atomisation and also the proportionate loss in can pressure as the can empties is less. This helps maintain spray quality and flow rate better during can lifetime.
The valve assembly 3 comprises a generally cylindrical, axially movable valve stem 7 having an axial bore 8 extending from the upper end of valve stem 7 part way towards the lower end thereof. At its lower (proximal) end, valve stem 7 locates within a cylindrical housing 9 positioned internally of the container 2 and at its upper (distal) end is fitted with an actuator in the form of a cap 10 having a spray outlet region 11. Provided at the outlet end of region 11 is a conventional MBU (Mechanical Break-Up Unit) insert 13. The valve assembly 3 is secured to the top of the container 2 by means of a metallic top cap 30 which is crimped at a central portion to the upper end of the valve housing 9 and crimped at an outer periphery to the upper rim 2a of the container. An outer gasket (not shown) would typically be secured in place between the upper rim 2a and the outer periphery of the top cap 30 to ensure a hermetic seal.
In broad outline, the aerosol spray device 1 is operated by pressing down on the cap 10 to cause downward movement of valve stem 7 to an “open” position with resultant discharge of a spray from spray outlet region 11. As shown in the drawings, valve stem 7 is biased upwardly of the container 2 by means of a coil spring 14. Lower end of coil spring 14 locates around an aperture 16 in lower wall 17 of the housing 9. Depending from wall 17 is a tubular spigot 18 having a lower enlarged end 19 to which is fitted a dip tube 20 which extends to the base of the container 2. It will be appreciated from the drawing that the lower region of container 2 is in communication with the interior of the housing 9 via the dip tube 20, spigot 18 and aperture 16 (which provides a liquid inlet for housing 9).
In certain embodiments disclosed in WO 2011/061531 and WO 2011/128607, such as that illustrated in accompanying FIG. 1, the valve assembly includes a pair of sealing gaskets: a first 23 dedicated to sealing liquid inlets 28 to the stem; and a second 21 dedicated to sealing gas inlets 29 to the stem. The annular gaskets 22 and 23 are formed of rubber or other elastomeric material and are dimensioned to seal against the outer surface of valve stem 7. Formed in the wall of the housing 9 between the two gaskets 22 and 23 are a plurality of ports 24 which provide for communication between the pressurised gas in the head space 6 and an annular clearance 21a. 
The liquid feed passageways 28 and gas bleed inlet passageways 29 are axially spaced from each other by a distance such that, in the “rest” condition (“closed” position) of the aerosol as shown in FIG. 1, the passageways 29 are sealed by upper gasket 22 and passageways 28 are sealed by lower gasket 23. The cross-sections of the passageways 28 and 29 together with the axial spacing between these passageways and the dimensions of the upper and lower gaskets 22 and 23 are such that on depression of the valve stem 7 to the open position the gas bleed inlet passageways 29 are opened simultaneously with (or more preferably just before) the liquid feed passageways 28, thereby causing the generation of bubble laden flow in the outlet conduit 8 for supply to the spray outlet region 11 for discharge therefrom in the form of a fine aerosol.
In certain other embodiments disclosed in WO 2011/061531 and WO 2011/128607, such as illustrated in accompanying FIG. 2, a single gasket 23 is used to seal both the liquid inlet 72 to the stem and the gas inlet 71 to the stem. On movement of the valve stem 7 from the closed position to the open position, the stem inlets 71, 72 are moved proximally of the gasket 23 and are therefore brought into fluid communication with, respectively, a gas inlet 73 in the housing 9, and a liquid inlet 16 in the housing, thereby causing the generation of bubble laden flow in the outlet conduit 8. Further examples of single gasket embodiments are shown and described by reference to FIGS. 9a to 16 of WO 2011/128607, one example of which is shown in the accompanying FIGS. 3a to 3c, in which the single gasket 23 is in fact formed in two adjacent parts: a thin gasket 112 and an annular seal 111, supported in the housing by a support ring 110.
The thin gasket 112 is shown in greater detail in FIG. 3c and comprises a disc having a central aperture 113 that is sized to be a close fit about the valve stem 7. A radial groove 123a extends in one side of the disc from the central aperture to an edge of the disc, where the groove connects with an axial notch 123b that extends through the edge of the disc. The groove 123a and notch 123b together comprise a gas inlet port that forms a gas flow path from the headspace 6 to the gas bleed inlet 121 when the valve stem is depressed, as in FIG. 3b. A notch 124 extends through the disc 112 at a point at the edge of the aperture 113 diametrically opposite to the groove 123a. When the valve stem is depressed, the notch 124 forms a liquid flow path between the annular clearance 21 and the liquid feed inlet 122. The annular clearance 21 is in fluid communication with the liquid inlet 16 in the housing via an axial channel 106 through the lower portion of the valve stem 7 and a transverse opening 108 located at the upper end of the channel 106.
FIG. 3a shows the valve stem 7 of this exemplary known single gasket valve assembly in a closed position, in which the valve stem 7 is extended out of the housing 9, under the action of the spring 14, so that the gas bleed inlet(s) 121 and the liquid inlets(s) 122 are each on the opposite (distal) side of the seal 23 to the gasket 112, or are at least blocked by the seal.
An advantage of a single gasket arrangement is that it employs fewer parts and thus reduces material, manufacturing and assembly costs in comparison to double gasket arrangements. Additionally, it may readily be produced in dimensions well suited to manufacture with the same overall dimensions as conventional liquefied gas propellant aerosol valves. However, in such known single gasket arrangements, there is a risk that the gasket may swell from contact with the liquid contents 5 of the spray device, at least for certain liquids. Such swelling would increase the friction between the gasket 23 and the valve stem 7, which could lead to the valve stem becoming stiffer to move or even becoming stuck. Also, in order to ensure that the stem gas and liquid inlets are brought into fluid communication with their associated housing gas and liquid inlets on movement of the stem 7 to the open position, it has been necessary to include features, such as the stem lugs 7a and associated housing grooves 9a of FIG. 3b, to prevent rotation of the valve stem 7 in the housing 9, and to account for proper orientation of the valve stem during assembly.
It is therefore an object of the invention to provide a single gasket valve arrangement in which the liquid contents of the spray device are kept out of contact with the gasket. It is a further object of the invention to provide a single gasket valve arrangement in which the valve stem can be rotated to any position and still function.